Surface microhardness of enamel after different home bleaching procedures

Objectives The purpose of this study was to evaluate the influence of different home bleaching procedures on surface microhardness of human enamel. Methods Among eight groups 192 incisors were distributed. The facial surface of each incisor was polished and baseline hardness of enamel (m0; Knoop) was assessed with a load of 1 N for 30 s. Subsequently, the enamel was treated for 14 days with the bleaching agent: groups 1, 2 and 4 Viva Style Paint on, 8% carbamide peroxide (CP) 1 × 20 min, 2 × 20 min and 2 × 5 min; group 3 Colgate Simply White, 5.9% hydrogen peroxide (HP), 2 × 30 min; group 5 Viva Style 10% CP 1 × 1 h; group 6 Blend-a-med White Strips, 5.9% HP 2 × 30 min; group 7 Odol-med3 Beauty-Kur, sodium chlorite 2 × 10 min; group 8 control, running water 1 × 1 h. Hardness was reassessed after the last bleaching treatment (m1) and after 6 weeks storage in artificial saliva (m2). Results Changes in microhardness were as follows (m0–m1): (1) −2.3 (±20.3); (2) −8.9 (±27.2); (3) 63.4 (±56.3); (4) 9.6 (±30.1); (5) 12.8 (±62.6); (6) 92.2 (±50.2); (7) 158.4 (±59.7); (8) 10.6 (±38.5). Statistical analysis showed that hardness values were significantly (p ≤ 0.0005; Wilcoxon test) reduced in groups 3, 6, and 7 (m1) and in group 7 (m2). Significance Both type of bleaching agent and concentration have a significant influence on the microhardness of enamel. The most critical bleaching agent seems to be the one containing sodium chlorite in combination with citric acid.